I thought I could haul serious coin buying first-year toys and other items related to Tim Burton's The Nightmare Before Christmas, as officially known. There weren't a lot of items back then. And I also predicted... correctly... when I saw the film as a new release, despite meh box-office performance, that it had strong potential to become a cult film.
What I didn't foresee was that once it got cult-film status, Disney would start cranking out dozens of items in all price ranges to sell every year then and since... in effect gutting the value of my "investment."
Sports collectors... see any parallels here??
I know, it seems obvious now, but take it from me, back then, Disney's hypercranking of TBNBC merch wasn't predictable. The problem was Disney, the studio that debated even releasing vs. spiking their film.
As with buying stocks, real estate etc., you can be 100% right in reading the market based on what you know at the time you buy and still not get what you expect years later because of forces beyond your control. There's no small measure of luck here.
We've also seen a general decline in the value of most collectibles in the last decade due to lower personal disposable income except among the 1%, combined with a general Boomer inclination desire to Downsize. Having dealt with trying to clean out the crap from my parents' and my wife's parents' personal belongings, I'm all in with that. I do not wish that pain on my children. If you think you're doing them a financial favor by amassing collection(s), eeeeeeeeeeeeh... I dunno.